1. Field
Aspects of embodiments of the present invention relate to radio-frequency (RF) transceivers, and, in particular, transmit-receive switching circuits of RF transceivers and a method of manufacturing the same.
2. Description of Related Art
An RF transceiver is a component of a wireless communication apparatus. The RF transceiver includes both a transmitter and a receiver in a single unit. When the transmitter and receiver share a common antenna for transmitting and receiving an RF signal, a transmit-receive (T/R) switch may be used to allow the transmitter and receiver to use the same antenna in a time-multiplexed fashion.
FIG. 1 is a block diagram illustrating an RF transceiver 100 including a T/R switch 101, a transmitter 103, and a receiver 105. In this RF transceiver embodiment, the T/R switch 101 functions as a single pole double throw device that connects an antenna 107 either to the transmitter 103 or to the receiver 105. In an implementation of the T/R switch 101, the considerations include size, cost, insertion loss, power handling, and power consumption of the switch. For example, the T/R switch 101 may be implemented as a solid state switch such as bipolar junction transistor (BJT), field effect transistor (e.g., J-FET, MOSFET, etc.) or PIN diode. A PIN diode is generally smaller and cheaper than a transistor; however, the PIN diode presents a high impedance to RF frequencies unless the PIN diode is biased with a DC bias current. As such, a switch implemented by PIN diode generally consumes more DC power than one implemented by a transistor such as a FET. When the PIN diode is biased with a DC bias current, the diode is turned on and provides a low resistance RF path between the anode and the cathode of the diode. On the other hand, a FET is controlled to turn on or off by applying a control voltage to its gate with insignificant DC gate current being drawn.
The RF transceiver may be implemented as an integrated circuit, where the active switches, (e.g., BJT and FET transistors or PIN diodes) of the T/R switch are typically stacked together in the shunt to ground in order to increase the high power handling capability through voltage division across the switches of the stack. However, in an integrated circuit, the active switches are not ideal circuits and each includes parasitic components depending on the structures and topologies of the active switches. Consequently, these parasitic components cause non-uniform voltage division among the active switches of the stack, thereby degrading the power handling capacity of the stack.
Known methods to equalize the voltages across the active switches utilize capacitors connected in parallel with the active switches to reduce the impedance of a particular switch and therefore reduce the voltage drop across the switch. However, these methods reply on discrete capacitors or separate capacitors that are monolithically attached across the terminals of each active switch (e.g., across a FET's drain and source terminals), thereby increasing the complexity, size, and cost of the switch circuit.